There is a need for adsorbent filters that can be conveniently used as molecular sieves to selectively and stably eliminate undesired solutes from liquids. The solutes to be filtered out may include pollutants or materials considered unhealthy or otherwise undesirable by persons who intend to consume the liquids or other compositions in which the solute is present.
The practice in the past has focused on reacting the targeted molecule to be removed with another binding chemical followed by a separation step, such as precipitation, centrifugation, or co-crystallization, and so forth. The addition of other compounds or molecules to the media to react or complex with the target substrate is usually tedious, timely consuming, and can not fully remove all of the added reactant and substrates in the product media.
A porous membrane with molecular sieving characteristics based on matrices of cellulose has been described by Mintova et al. (Zeolites 16 (1996) 31). Cellulose-based soft membranes of Y and L zeolites (i.e., aluminosilicates) have been prepared by Vu et al. (Microporous and Mesoporous Materials 55 (2002) 93–101).
Cellulose/silica composites have found applications in cosmetics (e.g., tissue conditioner) (Nikawa et al., J. Oral Rehabil. 24 (1997) 350); fabric softeners (EPO Pat. No. 1,061,124 (2000)); medical fields (e.g., antibacterial materials and protection of denture plaque) (Nikawa, J. Oral Rehabil. 24 (1997) 350); and for removal of foul smells (e.g., NH3, H2S, and EtNH2) (JP Pat. No. 63,224,734 (1988); JP Pat. No. 86,241,059 (1988)).
These materials also can be used for filtration as ultra filtration membranes (Mara et al., J. Membr. Sci. 36 (1988) 277); tobacco smoke filters (U.S. Pat. No. 3,327,718); in water purification (JP Pat. 92,286,299 (1994)); and in air purification (JP Pat. 92,129,440 (1993)).
Prior methods for making adsorbent composites of fibers and absorbent mineral particles like zeolite, or silica, have involved the use of adhesive polymers. JP Pat. 2,000, 189, 793 (2000); Fujio, M., Hyomen Kagaku 19 (1998) 658; Sano et al., Proc. Int. Zeolite Conf., 9th (1993) 239–246. The adhesion method has several disadvantages. Mintova et al., Preparation of Zeolite-Covered Cellulose Fibers, 209th National Meeting Abstracts, American Chemical Society, (1995). The major disadvantages include the possibility of the adhesive dissolving, totally or partially during filtration, and/or might potential interference with the selective adsorption process.
Another prior method for making the fiber/absorbent particle types of composites has involved the use of electret technology, such as described in U.S. Pat. No. 5,906,743 (1993). However, electret technology can pose an occupational hazard due to the use of high voltage to adhere inorganic solids onto charged cellulose fibers.
Molecular imprinting is a method used to design materials for special, highly selective separation processes. A benefit of imprinted materials is the possibility to prepare the sorbents to target a specific molecule or functional groups. Since molecular recognition is emerging as a potentially useful concept in biological and chemical processes, considerable efforts have been made to prepare such materials during the past decade. See, e.g., Lehn et al., Chem., Int. Ed. Engl. (1990), 29, 1304–1319; Fabbrizzi et al., Amer. Chem. Soc. Rev. (1995), 197–202. Silica is a well known as a high surface area heterogeneous catalyst support and sorbent. Silica gel prepared in the presence of specific dye molecule (“template”) shows an increased affinity for the same dye after its removal from the silica matrix. Dickey, Proc. Natl. Acad. of Sci. (1949), 35, 227–229.
A “footprint” technique has also been developed using tailor-made catalysts specific for trans-acylation; the catalysts were prepared by imprinting hypothesized transition-state analogues onto alumina ion-doped silica gels. Morihara et al., J. Bull. Chem. Soc. Jpn. (1988), 61, 3991–3998; Morihara et al., T. Bull. Chem. Soc. Jpn. (1994), 67, 1078–1084. Polymerized organic silanes have been used on the surface of porous silica particles in aqueous solutions to provide a soft layer for imprinting. Glad et al., Chromatogr. (1985), 347, 11–23. Imprinted materials have found applications in the preparation of highly selective chemical sensors. Kriz, D., et al., Anal. Chim. Acta 336 (1997) 345A; Malitesta et al., Anal. Chem. 71 (1999) 1366; Kobayashi, Chem. Lett. 927 (1995). They also have been used in controlled transport membranes. Krotz et al., J. Am. Chem. Soc. 118 (1996) 8154; Yoshikawa et al., J. Membr. Sci. 108 (1995) 171; Wang, et al., Langmuir 12 (1996) 4850; Bartsch et al., Molecular and Ionic Recognition with Imprinted Polymers, in: ACS Symposium Series 703, American Chemical Society, Washington, D.C., USA, (1998) p. 188. They additionally have been used in radioimmunoassays. Vlatakis et al., Nature (London) (1993) 361 645–647.
Molecular imprinted silicas also have been used as catalyst in stereo selective and regioselective reactions. Shea et al., J. Org. Chem. 1978 43 4253–4255; Damen et al., Tetrahedron Lett. (1980) 21 1913–1916. In further developments, layers of cross-linked polysiloxanes were produced in the presence of template molecules on previously prepared silica gel particles. A somewhat different approach, which does not rely on such layer-by-layer techniques, consists of direct adsorption of the imprinting molecule. Morihara et al., J. Bull. Chem. Soc. Jpn. (1988), 61, 3991–3998; Morihara et al., J. Chem. Soc. Chem. Commum. (1992) 358–360. However, loose granulated silica materials are not convenient for handling, use, and/or disposal in filter operations involving filtration of solutes from hot fluids.
A need still exists for self-supporting stable filters having matrices that do not structurally degrade, nor suffer from loss of adsorbent, to the extent the filter function is impaired when the filter is used in the presence of hot liquid filtrates. A need also exists for an approach to making adsorbent filters that avoids the need for extraneous substances, such as polymeric adhesives, to integrate the adsorbent and matrix.
As will become apparent from the descriptions that follow, the present invention addresses these needs as well as offers other advantages and benefits.